Growth, Fabrication and Characterization of GaN-based Bipolar Transistors

Dr. Huili Xing
University of California, Santa Barbara

GaN-based bipolar transistors promise applications in power electronics like the more-established AlGaN/GaN high electron mobility transistors (HEMTs), owing to the high breakdown fields, the large electron saturation velocity, and the large band offsets of the III-V nitride semiconductors. Because of immature processing techniques and difficulties associated with controlled p-type doping of GaN, it has been difficult to fabricate GaN based bipolar transistors.

Poor ohmic contacts and high leakage currents between terminals complicate the characterization of GaN based bipolar transistors. We have found that the anomalously high at low current levels observed by many groups was not the gain of the intrinsic device, but an artifact of the effects of leakage coupled with non-ohmic contacts. Our work has cleared the ambiguity in the literature and provided a guideline for proper characterization of bipolar transistors with poor terminal contacts. The extensive analysis on device current gain reveals that currently GaN-based bipolar transistor performance is limited by a short minority carrier lifetime in the base at intermediate current levels and by the Kirk effect at high current levels.

Improved understanding gained from studies of growth and processing has led us to demonstrate record performance for GaN-based bipolar transistors. The output current is as high as ~ 50 mA (??~ 10) and the current gain is as high as ~ 20 (IC ~ 20 mA). The breakdown voltage of ~ 470 V was demonstrated but it is still limited by premature surface breakdown.

Friday, April 2nd, 2 pm
CHTM room 101

(Center for High Technology Materials, 1313 Goddard SE, at south campus of UNM, can be reached by shuttle, 272-7800)

Download announcement as PDF file.